This invention relates to hydraulic apparatus and, more particularly, to hydraulic pumps and/or motors of the axial piston type.
An axial piston pump of the type with which the present invention is concerned includes a set of angularly spaced pistons adapted to reciprocate in a rotatable cylinder block. An inclined swash plate is rotated by an input shaft and causes the pistons to reciprocate within the cylinder block. During the intake stroke of each piston, charge oil is delivered to the cylinders under the control of a valve block. The charge oil is pressurized during the power stroke of each piston and is discharged at high pressure through the valve block. The displacement of the pump may be selectively varied by changing the angle of the swash plate.
An axial piston hydraulic motor similarly includes a rotatable cylinder block, a set of angularly spaced pistons adapted to reciprocate in the block and a swash plate connected to the pistons. The pistons are reciprocated as oil is admitted into and exhausted from the cylinders under the control of a valve block, such reciprocation effecting rotation of the swash plate and an output shaft connected to the swash plate.
A hydrostatic drive may be formed by arranging a pump and motor in tandem with their cylinder blocks located on opposite sides of a rotationally stationary valve block. In such an instance, the pump driven by the input shaft pressurizes charge oil and delivers high pressure oil to the motor to drive the output shaft.
Hydraulic apparatus of the foregoing type inherently produces noise. Oil flowing between the cylinder blocks and the valve block for flow into and out of the cylinders causes the cylinder block to pulsate with respect to the valve block. Such pulsations produce noise and reduce the smoothness and efficiency of the apparatus.